Eccentricity (mathematics)
![All types of conic sections, arranged with increasing eccentricity. Note that curvature decreases with eccentricity, and that none of these curves intersect.](/Images/godic/202502/09/Eccentricity.svg4939.png")
![plane section of a cone](/Images/godic/202502/09/Exzentr3d-s.svg4939.png")
![Ellipse and hyperbola with constant a and changing eccentricity e.](/Images/godic/202502/09/Ellipse_and_hyperbola4939.gif")
![Ellipses, hyperbolas with all possible eccentricites from zero to infinity and a parabola on one cubic surface.](/Images/godic/202502/09/Cubic_surface4939.gif")
In mathematics, the eccentricity, denoted e or ![\varepsilon](/Images/godic/202502/09/c691dc52cc1ad756972d4629934d37fd4939.png")
, is a parameter associated with every conic section. It can be thought of as a measure of how much the conic section deviates from being circular.
In particular,
Furthermore, two conic sections are similar (identically shaped) if and only if they have the same eccentricity.